Re: [6.2 regression][bisected]discard storm on idle since v6.1-rc8-59-g63a7cb130718 discard=async

David Sterba
2023-04-11T17:52:54Z

On Mon, Apr 10, 2023 at 03:03:37AM +0100, Michael Bromilow wrote:
> On 04/04/2023 19:51, Boris Burkov wrote:
> > On Tue, Apr 04, 2023 at 02:15:38PM -0400, Chris Mason wrote:
> >> So, honestly from my POV the async discard is best suited to consumer
> >> devices. Our defaults are probably wrong because no matter what you
> >> choose there's a drive out there that makes it look bad. Also, laptops
> >> probably don't want the slow dribble.
> >
> > Our reasonable options, as I see them:
> > - back to nodiscard, rely on periodic trims from the OS.
> > - leave low iops_limit, drives stay busy unexpectedly long, conclude that
> > that's OK, and communicate the tuning/measurement options better.
> > - set a high iops_limit (e.g. 1000) drives will get back to idle faster.
> > - change an unset iops_limit to mean truly unlimited async discard, set
> > that as the default, and anyone who cares to meter it can set an
> > iops_limit.
> >
> > The regression here is in drive idle time due to modest discard getting
> > metered out over minutes rather than dealt with relatively quickly. So
> > I would favor the unlimited async discard mode and will send a patch to
> > that effect which we can discuss.
>
> Will power usage be taken into consideration? I only noticed this regression
> myself when my laptop started to draw a constant extra ~10W from the constant
> drive activity, so I imagine other laptop users would also prefer a default
> which avoids this if possible. If "relatively quickly" means anything more
> than a few seconds I could see that causing rather significant battery life
> reductions.

This may need to be configured from userspace, e.g. from
laptop-mode-tools, I'm not sure if any of the power usage info is
available from kernel.